Liquid crystal display device and manufacturing method thereof, and electronic device

ABSTRACT

An objective is simplification of a manufacturing method of a liquid crystal display device or the like. In a manufacturing method of a thin film transistor, a stack in which a first conductive film, an insulating film, a semiconductor film, an impurity semiconductor film, and a second conductive film are stacked in this order is formed, and the first conductive film is exposed by first etching and a pattern of the second conductive film is formed by second etching. Further, after thin film transistors are formed, a color filter layer is formed so that unevenness caused by the thin film transistors or the like is relieved; thus, the level difference of the surface where the pixel electrode layer is formed is reduced. Alternatively, a color filter layer is selectively formed utilizing the unevenness caused by thin film transistors or the like.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device, amanufacturing method of the liquid crystal display device, and anelectronic device using the liquid crystal display device.

BACKGROUND ART

In recent years, thin film transistors that are formed using asemiconductor thin film having a thickness of several nanometers toseveral hundreds of nanometers over a substrate having an insulatingsurface such as a glass substrate have been attracting attentions. Thinfilm transistors are widely used for electronic devices such asintegrated circuits (IC) and electro-optical devices. In particular,thin film transistors are urgently developed as switching elements ofimage display devices typified by liquid crystal display devices, EL(electro luminescence) display devices, and the like. In an activematrix liquid crystal display device, specifically, a voltage is appliedbetween a pixel electrode connected to a switching element and anopposite electrode corresponding to the pixel electrode, and thus, aliquid crystal layer disposed between the pixel electrode and theopposite electrode is modulated optically. The optical modulation can berecognized as a display pattern by an observer. An active matrix liquidcrystal display device here means a liquid crystal display device whichemploys a method in which a display pattern is formed on a screen bydriving pixel electrodes arranged in matrix using switching elements.

The application range of the active matrix liquid crystal displaydevices is expanding, and demands for larger screen size, higherdefinition, and higher aperture ratio, and the like of such a liquidcrystal display device are increasing. In addition, a need exits for lowmanufacturing cost and high yield with respect to such an active matrixliquid crystal display device as well as high reliability. As a methodfor increasing productivity and reducing manufacturing cost,simplification of the process can be given.

In an active matrix liquid crystal display device, thin film transistorsare mainly used as switching elements. In order to simplify amanufacturing process of thin film transistors, reduction in the numberof photomasks used in photolithography is effective. If one photomask isadded, for example, the following steps are required: resistapplication, prebaking, light exposure, development, postbaking, and thelike, and moreover other steps before and after the aforementionedsteps, such as film formation and etching and further resist removal,cleaning, drying, and the like. The number of steps is significantlyincreased only by adding one photomask in the manufacturing process.Thus, a process is simplified or complicated depending on the number ofphotomasks; therefore, many technical developments are made so as toreduce the number of photomasks used in a manufacturing process.

Many conventional techniques for reducing the number of photomasks use acomplicated technique such as backside light exposure, resist reflow, ora lift-off method, which requires a special apparatus. There has been aconcern that yield is reduced due to various problems caused by usage ofsuch a complicated technique. Moreover, there has often been no optionbut to sacrifice electrical characteristics of thin film transistors.

As typical means for reducing the number of photomasks in amanufacturing process of a thin film transistor, a technique using amulti-tone mask (called a halftone mask or a gray-tone mask) is widelyknown. As a technique for reducing the number of manufacturing steps byusing a multi-tone mask, Patent Document 1 (Japanese Published PatentApplication No. 2003-179069) is, for example, disclosed.

DISCLOSURE OF INVENTION

It is an object to simplify the manufacturing process of a thin filmtransistor, and thereby simplifying the manufacturing process of aliquid crystal display device. It is another object to provide amanufacturing method of a liquid crystal display device, in whichproblems caused in the above manufacturing method are solved. It isstill another object to provide a manufacturing method of a liquidcrystal display device, in which a feature of the above manufacturingmethod is effectively used.

To accomplish the above objects, in the invention to be disclosed, astack in which a first conductive film, an insulating film, asemiconductor film, an impurity semiconductor film, and a secondconductive film are stacked in this order is formed, and the firstconductive film is exposed by first etching and a pattern of the firstconductive film is formed by second etching. The first conductive filmis side-etched at the time of second etching, which makes it possible todifferentiate a pattern (a pattern of the first conductive film) formedby the second etching from a pattern (patterns of the insulating film,the semiconductor film, the impurity semiconductor film, and the secondconductive film) formed by first etching. Thus, the number of photomasksis reduced and the process is simplified. Further, after thin filmtransistors are formed, a color filter layer is formed so thatunevenness caused by the thin film transistors or the like is relieved;thus, the level difference of the surface where the pixel electrodelayer is formed is reduced. Alternatively, a color filter layer isselectively formed utilizing the unevenness caused by thin filmtransistors or the like. More specific solutions will be describedbelow.

A manufacturing method of a liquid crystal display device of theinvention to be disclosed includes sequentially forming and stacking afirst conductive film, a first insulating film, a semiconductor film, animpurity semiconductor film, and a second conductive film; forming aresist mask having a recessed portion over the second conductive film;performing first etching on the first insulating film, the semiconductorfilm, the impurity semiconductor film, and the second conductive filmusing the resist mask, thereby exposing at least the first conductivefilm; performing second etching involving side etching on part of thefirst conductive film, thereby forming a gate electrode layer; etchingthe recessed portion of the first resist mask thereby exposing a regionof the second conductive film, which overlaps with the recessed portionof the first resist mask; performing third etching on part of the secondconductive film, the impurity semiconductor film, and the semiconductorfilm using the resist mask which has been etched, thereby forming asource electrode layer, a drain electrode layer, a source region layer,a drain region layer, and a semiconductor layer; after removing theresist mask, forming a second insulating film so as to cover a thin filmtransistor including the source electrode layer, the drain electrodelayer, the source region layer, the drain region layer, and thesemiconductor layer; forming a color filter over the second insulatingfilm; and forming a pixel electrode layer over the color filter layer.Further, unevenness of a surface on which the pixel electrode layer isformed is reduced using the color filter layer.

Another manufacturing method of a liquid crystal display device of theinvention to be disclosed includes sequentially forming and stacking afirst conductive film, a first insulating film, a semiconductor film, animpurity semiconductor film, and a second conductive film; forming afirst resist mask over the second conductive film; performing firstetching on the first conductive film, the first insulating film, thesemiconductor film, the impurity semiconductor film, and the secondconductive film using the first resist mask, thereby exposing at leastthe first conductive film; performing second etching involving sideetching on part of the first conductive film, thereby forming a gateelectrode layer; after removing the first resist mask, forming a secondresist mask; performing third etching on part of the second conductivefilm, the impurity semiconductor film, and the semiconductor film usingthe second resist mask, thereby forming a source electrode layer, adrain electrode layer, a source region layer, a drain region layer, anda semiconductor layer; after removing the second resist mask, forming asecond insulating film so as to cover a thin film transistor includingthe source electrode layer, the drain electrode layer, the source regionlayer, the drain region layer, and the semiconductor layer; forming acolor filter over the second insulating film; and forming a pixelelectrode layer over the color filter layer. Further, unevenness of asurface on which the pixel electrode layer is formed is reduced usingthe color filter layer.

Another manufacturing method of a liquid crystal display device of theinvention to be disclosed includes sequentially forming and stacking afirst conductive film, a first insulating film, a semiconductor film, animpurity semiconductor film, and a second conductive film; forming aresist mask having a recessed portion over the second conductive film;performing first etching on the first insulating film, the semiconductorfilm, the impurity semiconductor film, and the second conductive filmusing the resist mask, thereby exposing at least the first conductivefilm; performing second etching involving side etching on part of thefirst conductive film, thereby forming a gate electrode layer; makingthe first resist mask recede, thereby exposing a region of the secondconductive film, which overlaps with a recessed portion of the firstresist mask; performing third etching on part of the second conductivefilm, the impurity semiconductor film, and the semiconductor film usingthe resist mask which has been etched, thereby forming a sourceelectrode layer, a drain electrode layer, a source region layer, a drainregion layer, and a semiconductor layer; after removing the resist mask,forming a second insulating film so as to cover a thin film transistorincluding the source electrode layer, the drain electrode layer, thesource region layer, the drain region layer, and the semiconductorlayer; selectively forming a color filter over the second insulatingfilm; and forming a pixel electrode layer over the color filter.

Another manufacturing method of a liquid crystal display device of theinvention to be disclosed includes forming a first conductive film, andforming an insulating film over the first conductive film, and forming asemiconductor film over the insulating film, and forming an impuritysemiconductor film over the semiconductor film, and forming a secondconductive film over the impurity semiconductor film, and forming afirst resist mask including a recessed portion, over the secondconductive film, and first etching the insulating film, thesemiconductor film, the impurity semiconductor film, and the secondconductive film using the first resist mask to expose at least a surfaceof the first conductive film, and second etching a portion of the firstconductive film to form a gate electrode layer in such manner that awidth of the gate electrode is narrower than a width of the insulatingfilm, and forming a second resist mask by etching the recessed portionof the first resist mask to expose a part of the second conductive filmoverlapping with the recessed portion of the first resist mask, andthird etching the second conductive film, the impurity semiconductorfilm, and a part of the semiconductor film using the second resist maskto form a source and drain electrode layer, source and drain regionlayers, and a semiconductor layer, and after removing the second resistmask, forming a second insulating film over the source electrode layer,the drain electrode layer, the source region layer, the drain regionlayer, and the semiconductor layer, and forming a color filter over thesecond insulating film, and forming a pixel electrode layer over thecolor filter.

Note that the resist mask whose upper surface has a recessed portion ispreferably formed using a multi-tone mask. Further, the color filterlayer may be selectively formed by a printing method, an ink-jet method,or the like.

Note that, by side etching, a gate electrode layer whose side surface isformed inner than a side surface of the first insulating layer by apredetermined distance can be formed. Further, it is preferable thatfirst etching is performed by dry etching and second etching isperformed by wet etching. This is because the processing by the firstetching is preferably performed with high precision, and side etchingneeds to be performed in the processing by the second etching.

Liquid crystal display devices and electronic devices having the liquidcrystal display devices can be provided by using the manufacturingmethod of a liquid crystal display device.

Note that the “pattern of the first conductive film” means, for example,a top view layout of a metal wiring which forms a gate electrode, a gatewiring, a capacitor electrode, and a capacitor wiring.

Note that in this specification, “corrosion” refers to unintentionaletching in the processing by an etching. Therefore, etching ispreferably performed under conditions where corrosion is reduced to aminimum.

Note that in this specification, a “gate wiring” means a wiringconnected to a gate electrode of a thin film transistor. The gate wiringis formed using a gate electrode layer. Further, the gate wiring issometimes referred to as a scan line.

Note that in this specification, a “source wiring” is a wiring connectedto a source/drain electrode of a thin film transistor. The source wiringis formed using a source/drain electrode layer. Further, the sourcewiring is sometimes referred to as a signal line.

With the use of the present invention to be disclosed, the number ofsteps for manufacturing thin film transistors can be significantlyreduced. In other words, a manufacturing process of a liquid crystaldisplay device can be simplified. Note that in the conventionaltechnique which is aimed at reducing the number of photomasks,electrical characteristics of thin film transistors have often beensacrificed; however, in the present invention to be disclosed, thenumber of steps for manufacturing a thin film transistor can besignificantly reduced while electrical characteristics of the thin filmtransistor are maintained.

Further, a color filter layer is formed so that unevenness caused by thethin film transistors or the like is relieved; thus, the leveldifference of the surface where the pixel electrode layer is formed canbe reduced. Thus, uniform voltage can be applied to liquid crystal, sothat orientation disorder is suppressed and favorable display isrealized. In the case of selectively forming a color filter layer usinga printing method, an ink-jet method, or the like, the color filters canbe formed separately by utilizing unevenness caused by thin filmtransistors or the like (for example, unevenness due to a sourcewiring); accordingly, accuracy of separate formation of the colorfilters is improved. Thus, the color filters can be favorably formedwithout employing a special structure.

Note that a thin film transistor manufactured by a manufacturing methodof the present invention has a cavity in contact with an end portion ofa gate electrode layer, so that leakage current between a gate electrodeand a drain electrode can be made low. Further, since the cavity isformed, the dielectric constant of the vicinity of the end portion ofthe gate electrode can be made low (low-k).

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 2A to 2C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 3A to 3C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 4A to 4C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 5A to 5C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 6A to 6C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 7A to 7C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 8A to 8C illustrate an example of a manufacturing method of a thinfilm transistor and a display device according to the present invention;

FIGS. 9A to 9C illustrate an example of a manufacturing, method of athin film transistor and a display device according to the presentinvention;

FIGS. 10A to 10C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 11A to 11C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 12A to 12C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 13A to 13C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 14A to 14C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 15A to 15C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIG. 16 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 17 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 18 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 19 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 20 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 21 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 22 illustrates a connection portion of an active matrix substrateobtained by applying a manufacturing method of the present invention isapplied;

FIG. 23 illustrates a connection portion of an active matrix substrateobtained by applying a manufacturing method of the present invention isapplied;

FIGS. 24A to 24C illustrate connection portions of active matrixsubstrates obtained by applying a manufacturing method of the presentinvention;

FIGS. 25A-1 and 25A-2 and FIGS. 25B-1 and 25B-2 each illustrate amulti-tone mask used for a manufacturing method of the presentinvention;

FIGS. 26A to 26C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 27A to 27C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIG. 28 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 29 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIG. 30 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIGS. 31A to 31C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 32A to 32C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 33A to 33C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 34A to 34C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 35A to 35C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIG. 36 illustrates an example of a manufacturing method of a thin filmtransistor and a display device according to the present invention;

FIGS. 37A to 37C illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 38A and 38B illustrate an example of a manufacturing method of athin film transistor and a display device according to the presentinvention;

FIGS. 39A and 39B are perspective views of electronic devices each usinga display device according to the present invention;

FIG. 40 illustrates an electronic device using a display deviceaccording to the present invention; and

FIGS. 41A to 41C illustrate an electronic device using a display deviceaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment Mode

Embodiment modes will be described in detail with reference to thedrawings. However, the present invention is not limited to the followingdescription, and it is readily appreciated by those skilled in the artthat modes and details of the present invention can be modified invarious ways without departing from the spirit and the scope of theinvention. Further, structures of different embodiment modes can beimplemented in combination as appropriate. Note that in a structure ofthe invention described below, like portions or portions having similarfunctions are denoted by the same reference numerals, and descriptionthereof will not be repeated. The same hatching pattern is applied tosimilar parts, and the similar parts are not especially denoted byreference numerals in some cases.

Embodiment Mode 1

In this embodiment mode, an example of a method for manufacturing asemiconductor device will be described with reference to FIGS. 1A to25B-2.

FIG. 16 to FIG. 20 are plan views of thin film transistors according tothis embodiment mode. FIG. 20 is a drawing of the situation in whichsteps up to and including the step of forming a pixel electrode havebeen finished. FIG. 1A to FIG. 3C are cross-sectional views taken alongline A-A′ in FIG. 16 to FIG. 20. FIG. 4A to FIG. 6C are cross-sectionalviews taken along line B-B′ in FIG. 16 to FIG. 20. FIG. 7A to FIG. 9Care cross-sectional views taken along line C-C′ in FIG. 16 to FIG. 20.FIG. 10A to FIG. 12C are cross-sectional views taken along line D-D′ inFIG. 16 to FIG. 20. FIG. 13A to FIG. 15C are cross-sectional views takenalong line E-E′ in FIG. 16 to FIG. 20.

First, a first conductive film 102, a first insulating film 104, asemiconductor film 106, an impurity semiconductor film 108, and a secondconductive film 110 are formed over a substrate 100. These films may bein a single layer or may be a film stack in which a plurality of filmsis stacked.

An insulating substrate can be used for the substrate 100. Insulatingsubstrates includes, for example, a glass substrate or a quartzsubstrate. In this embodiment mode, a glass substrate is used as thesubstrate 100.

The first conductive film 102 is formed of a conductive material. Thefirst conductive film 102 is formed using a conductive material such asa metal material, for example, titanium, molybdenum, chromium, tantalum,tungsten, aluminum, copper, neodymium, niobium, or scandium, or an alloymaterial including any of these metal materials as a main component.Note that the material of the first conductive film 102 needs to beselected from materials which have such heat resistance as to withstanda later step (such as formation of the first insulating film 104) andare not easily corroded or eaten in a later step (such as etching of thesecond conductive film 110). Only under these conditions, the materialof the first conductive film 102 is not limited to a particularmaterial.

In addition, the first conductive film 102 can be formed by, forexample, sputtering, a CVD method (including thermal CVD, plasma CVD,and the like), or the like. However, the formation method of the firstconductive film 102 is not limited to a particular method.

The first insulating film 104 serves as a gate insulating film, which isformed of an insulating material. The first insulating film 104 can beformed using, for example, a silicon oxide film, a silicon nitride film,a silicon oxynitride film, a silicon nitride oxide film, or the like.Note that similar to the first conductive film 102, the material of thefirst insulating film 104 needs to be selected from materials whichresist a certain level of heat and are not easily corroded or eaten in alater step. Only under these conditions, the material of the firstinsulating film 104 is not limited to a particular material.

In addition, the first insulating film 104 can be formed by, forexample, a CVD method (including thermal CVD, plasma CVD, and the like),sputtering, or the like; however, the formation method of the firstinsulating film 104 is not limited to a particular method.

The semiconductor film 106 is formed of a semiconductor material. Thesemiconductor film 106 can be formed using, for example, amorphoussilicon formed using a silane gas or the like. Note that similarly tothe first conductive film 102 and the like, the material of thesemiconductor film 106 needs to be selected from materials which resista certain level of heat and are not easily corroded or eaten in a laterstep. Only under these conditions, the material of the semiconductorfilm 106 is not limited to a particular material. Therefore, germaniumor the like may be used. Note that the crystallinity of thesemiconductor film 106 is not particularly limited either.

In addition, the semiconductor film 106 can be formed by, for example, aCVD method (including thermal CVD, plasma CVD, and the like),sputtering, or the like. However, the formation method of thesemiconductor film 106 is not limited to a particular method.

The impurity semiconductor film 108 is a semiconductor film containingan impurity element imparting one conductivity type, and is formed usinga semiconductor material gas to which the impurity element imparting oneconductivity type is added or the like. For example, the impuritysemiconductor film 108 is a silicon film containing phosphorus or boron,which is formed using a silane gas containing phosphine (chemicalformula: PH₃) or diborane (chemical formula: B₂H₆). Note that similarlyto the first conductive film 102 and the like, a material of theimpurity semiconductor film 108 needs to be selected from materialswhich resist a certain level of heat and are not easily corroded oreaten in a later step. Only under these conditions, the material of theimpurity semiconductor film 108 is not limited to a particular material.Note that the crystallinity of the impurity semiconductor film 108 isnot particularly limited either.

In the case of manufacturing an n-channel thin film transistor,phosphorus, arsenic, or the like may be used as the impurity elementimparting one conductivity type, which is to be added. That is, a silanegas used for the formation of the impurity semiconductor film 108 maycontain phosphine, arsine (chemical formula: AsH₃), or the like at apredetermined concentration. Alternatively, in the case of manufacturinga p-channel thin film transistor, boron or the like may be used as theimpurity element, which is to be added. That is, a silane gas used forthe formation of the impurity semiconductor film 108 may containdiborane or the like at a predetermined concentration.

In addition, the impurity semiconductor film 108 can be formed by, forexample, a CVD method (including thermal CVD, plasma CVD, and the like),or the like. However, the formation method of the impurity semiconductorfilm 108 is not limited to a particular method.

The second conductive film 110 is formed of a material which is aconductive material (a material given as the material of the firstconductive film 102) but is different from the material used for thefirst conductive film 102. Here, the “different material” means amaterial having a different main component. Specifically, a materialwhich is not easily etched by second etching which is described later ispreferably selected. Further, similarly to the first conductive film 102and the like, the material of the second conductive film 110 needs to beselected from materials which resist a certain level of heat and are noteasily corroded or eaten in a later step. Accordingly, only under theseconditions, the material of the second conductive film 110 is notlimited to a particular material.

In addition, the second conductive film 110 can be formed by, forexample, sputtering, a CVD method (including thermal CVD, plasma CVD,and the like), or the like. However, the formation method of the secondconductive film 110 is not limited to a particular method.

Next, a first resist mask 112 is formed over the second conductive film110 (see FIG. 1A, FIG. 4A, FIG. 7A, FIG. 10A, and FIG. 13A). The firstresist mask 112 is a resist mask whose upper surface has a recessedportion or a projecting portion. In other words, the first resist mask112 can also be referred to as a resist mask including a plurality ofregions having different thicknesses (here, two thicknesses).Hereinafter, with respect to the first resist mask 112, the thickerregion is called a projecting portion of the first resist mask 112 andthe thinner region is called a recessed portion of the first resist mask112.

The first resist mask 112 has a projecting portion in a region where asource/drain electrode layer is formed, and a recessed portion in aregion where the source/drain electrode layer is not formed and asemiconductor layer is exposed.

The first resist mask 112 can be formed using a multi-tone mask. Here,multi-tone masks will be described with reference to FIGS. 25A-1 to25B-2.

A multi-tone mask is a mask which makes it possible to perform lightexposure with multi-level light intensity, and typically, light exposureis performed with three levels of light intensity which provides anexposed region, a half-exposed region, and an unexposed region. Using amulti-tone mask, a resist mask with a plurality of thicknesses(typically, two thicknesses) can be formed through one-time process oflight exposure and development. Accordingly, using a multi-tone mask,the number of photomasks can be reduced.

FIG. 25A-1 and FIG. 25B-1 are cross-sectional views of typicalmulti-tone masks. FIG. 25A-1 illustrates a gray-tone mask 140 and FIG.25B-1 illustrates a half-tone mask 145.

The gray-tone mask 140 illustrated in FIG. 25A-1 includes alight-blocking portion 142 formed of a light-blocking film on asubstrate 141 which transmits light, and a slit portion 143 providedwith a pattern of the light-blocking film.

The slit portion 143 has slits (including dots, mesh, or the like)provided at intervals of equal to or less than the resolution limit oflight used for light exposure; thus, transmittance of light iscontrolled. Note that the slits provided at the slit portion 143 may beprovided periodically or aperiodically.

As the substrate 141 which transmits light, a substrate formed of amaterial of quartz or the like can be used. The light-blocking film forforming the light-blocking portion 142 and the slit portion 143 may beformed using a metal material and preferably formed using chromium,chromium oxide, or the like.

In the case where the gray-tone mask 140 is irradiated with light forlight exposure, as illustrated in FIG. 25A-2, the transmittance in theregion overlapping with the light-blocking portion 142 is 0%, and thetransmittance in the region where both the light-blocking portion 142and the slit portion 143 are not provided is 100%. Further, thetransmittance at the slit portion 143 is basically in the range of 10%to 70%, which can be adjusted with the interval of slits, or the like.

The half-tone mask 145 illustrated in FIG. 25B-1 includes asemi-light-transmitting portion 147 formed using asemi-light-transmitting film on a substrate 146 which transmits light,and a light-blocking portion 148 formed using a light-blocking film.

The semi-light-transmitting portion 147 can be formed using a materialof MoSiN, MoSi, MoSiO, MoSiON, CrSi, or the like. The light-blockingportion 148 may be formed using a metal material in a similar manner tothe light-blocking film of the gray-tone mask and preferably formedusing chromium, chromium oxide, or the like.

In the case where the half-tone mask 145 is irradiated with light forlight exposure, as illustrated in FIG. 25B-2, the transmittance in theregion overlapping with the light-blocking portion 148 is 0%, and thetransmittance in the region where both the light-blocking portion 148and the semi-light-transmitting portion 147 are not provided is 100%.Further, the transmittance in the semi-light-transmitting portion 147 isbasically in the range of 10% to 70%, which can be adjusted with thematerial to be used, its thickness, or the like.

When light exposure is performed using the multi-tone mask anddevelopment is performed, a first resist mask 112 having regions withdifferent thicknesses can be formed.

Next, first etching is performed using the first resist mask 112. Thatis, the first insulating film 104, the semiconductor film 106, theimpurity semiconductor film 108, and the second conductive film 110 areetched to form a thin film stack 114 (see FIG. 1B, FIG. 4B, FIG. 7B,FIG. 10B, FIG. 13B, and FIG. 16). At this time, at least the firstconductive film 102 is preferably exposed. In this specification, thisetching step is referred to as “first etching”. As the first etching,either dry etching or wet etching may be employed and a highlyanisotropic etching method is preferably performed. A highly anisotropicetching method is employed for the first etching; thus, the patternprocessing accuracy can be improved. Note that the first etching can beperformed by one step when dry etching is employed for the firstetching; meanwhile, the first etching is performed by a plurality ofsteps when wet etching is employed for the first etching, Thus, dryetching is preferably employed for the first etching.

Next, second etching is performed using the first resist mask 112. Thatis, the first conductive film 102 is etched to form a gate electrodelayer 116 (see FIG. 1C, FIG. 4C, FIG. 7C, FIG. 10C, FIG. 13C, and FIG.17). In this specification, such an etching step is referred to as“second etching.”

Note that the gate electrode layer 116 forms a gate wiring, a capacitorwiring, and a supporting portion. When a gate electrode layer isreferred to as a gate electrode layer 116A, the gate electrode layerforms a gate wiring; when a gate electrode layer is referred to as agate electrode layer 116B or a gate electrode layer 116D, the gateelectrode layer forms a supporting portion; and when a gate electrodelayer is referred to as a gate electrode layer 116C, the gate electrodelayer forms a capacitor wiring. Then, these gate electrode layers arecollectively referred to as the gate electrode layer 116.

The second etching is performed under such etching conditions that aside surface of the gate electrode layer 116 formed from the firstconductive film 102 is inner than a side surface of the thin film stack114. In other words, the second etching is performed so that the sidesurface of the gate electrode layer 116 is in contact with the bottomsurface of the thin film stack 114 (etching is performed so that thewidth of the gate electrode layer 116 is smaller than that of the thinfilm stack 114 in the cross section A-A′). It can be said that the gateelectrode layer 116 is provided so that its side surface is inner than aside surface of the first insulating film 104 (namely, a gate insulatinglayer) or the like. Further, the second etching is performed under suchconditions that the etching rate with respect to the second conductivefilm 110 is low and the etching rate with respect to the firstconductive film 102 is high. In other words, the second etching isperformed under the conditions that the etch selectivity of the firstconductive film 102 with respect to the second conductive film 110 ishigh. By performing the second etching under such conditions, the gateelectrode layer 116 can be formed.

As the second etching, either dry etching or wet etching may be employedand a highly isotropic etching method (chemical etching) is preferablyperformed. By employing a highly isotropic etching (chemical etching)method for the second etching, the first conductive film can beside-etched. Therefore, wet etching is preferably employed for thesecond etching.

Note that the shape of the side surface of the gate electrode layer 116is not particularly limited. For example, the shape may be a taperedshape. The shape of the side surface of the gate electrode layer 116 isdetermined depending on the conditions such as a liquid chemical used inthe second etching.

Here, the phrase “the conditions that the etching rate with respect tothe second conductive film 110 is low and the etching rate with respectto the first conductive film 102 is high” or “the conditions that theetch selectivity of the first conductive film 102 with respect to thesecond conductive film 110 is high” means conditions satisfying thefollowing first and second requirements.

The first requirement is that the gate electrode layer 116 is left in aplace where needed. The place necessarily provided with the gateelectrode layer 116 corresponds to regions indicated by dotted lines inFIG. 17 to FIG. 20. That is, it is necessary that the gate electrodelayer 116 is left so as to form a gate wiring, a capacitor wiring, and asupporting portion after the second etching. In order that the gateelectrode layer forms the gate wiring and the capacitor wiring, thesecond etching needs to be performed so as not to disconnect thesewirings. As illustrated in FIGS. 1A to 1C and FIG. 20, the gateelectrode layer 116 is provided so that its side surface is preferablyinner than the side surface of the thin film stack 114 by a distance d₁,and the distance d₁ may be set as appropriate by a practitioner inaccordance with the layout.

The second requirement is that a width d₃ of the gate wiring or thecapacitor wiring, which is formed by the gate electrode layer 116 and aminimum width d₂ of a source wiring formed by a source/drain electrodelayer 120A are appropriate (see FIG. 20). As the source/drain electrodelayer 120A is etched by the second etching, the minimum width d₂ of thesource wiring is reduced; accordingly, the current density of the sourcewiring becomes excessive and electrical characteristics are degraded.Therefore, the second etching is performed under the conditions that theetching rate of the first conductive film 102 is not too high and theetching rate of the second conductive film 110 is as low as possible. Inaddition, the second etching is performed under the conditions that theetching rate of the first conductive film 102 in third etching that willbe described subsequently is as low as possible.

It is difficult to make the minimum width d₂ of the source wiring large.This is because since the minimum width d₂ of the source wiring isdetermined depending on a minimum width d₄ of the semiconductor layeroverlapping with the source wiring, the minimum width d₄ of thesemiconductor layer has to be increased in order to make the minimumwidth d₂ of the source wiring larger, which makes it difficult toinsulate the gate wiring from the capacitor wiring, which are adjacentto each other. In the invention to be disclosed, the minimum width d₄ ofthe semiconductor layer is set smaller than about twice the distance d₁.In other words, the distance d₁ is set larger than about half theminimum width d₄ of the semiconductor layer.

It is accepted that there is at least one portion where the width of thesemiconductor layer overlapping with the source wiring is the minimumwidth d₄ between the gate wiring and the capacitor wiring which isadjacent to the gate wiring. It is preferable that the width of thesemiconductor layer in a region adjacent to the gate wiring and a regionadjacent to the capacitor wiring be the minimum width d₄ as illustratedin FIG. 20.

In addition, the width of the electrode in a portion connected to apixel electrode layer, which is formed of the source/drain electrodelayer, be equal to the minimum width d₂ of the source wiring.

As described above, the second etching under the condition where sideetching can be performed is very important in the invention to bedisclosed. This is because when the second etching involves side etchingof the first conductive film 102, the gate wiring and the capacitorwiring, which are adjacent to each other and are formed of the gateelectrode layer 116, can be insulated from each other (see FIG. 17).

Here, “side etching” means etching in which a film to be etched isetched in not only a thickness direction of the film (a directionperpendicular to the substrate surface or a direction perpendicular tothe surface of a base film of the film) but also in a directionperpendicular to the thickness direction (a direction parallel to thesubstrate surface or a direction parallel to the surface of the basefilm of the film). An end portion of the film which has been side-etchedcan have a variety of shapes depending on the etching rate of an etchinggas or a liquid chemical used for the etching with respect to the film.The film is formed so that, in many cases, its end portion has a curvedsurface.

As illustrated in FIG. 17, the thin film stack 114 formed by the firstetching is designed to be thin in a portion adjacent to a supportingportion which is formed by the gate electrode layer 116B or the gateelectrode layer 116D (see the portions indicated by the arrows in FIG.17). With this structure, the gate electrode layer 116A can bedisconnected to be insulated from the gate electrode layer 116B or thegate electrode layer 116D by the second etching.

The gate electrode layer 116B and the gate electrode layer 116D whichare illustrated in FIG. 17 each serve as a supporting portion whichsupports the thin film stack 114. With the supporting portion, peelingof a film such as a gate insulating film formed over the gate electrodelayer can be prevented. Further, with the supporting portion, a cavityregion formed adjacent to the gate electrode layer 116 by the secondetching can be prevented from being larger than necessary. Furthermore,it is preferable to provide the supporting portion because the thin filmstack 114 can be prevented from being broken or damaged due to its ownweight, and accordingly yield is increased. However, the presentinvention is not limited to the mode with the supporting portion, and astructure without the supporting portion can also be employed. Anexample of a plan view of the mode without the supporting portion(corresponding to FIG. 20) is illustrated in FIG. 21.

As described above, the second etching is preferably performed by wetetching.

In the case where the second etching is performed by wet etching,aluminum or molybdenum may be deposited as the first conductive film102, titanium or tungsten may be deposited as the second conductive film110, and a liquid chemical containing nitric acid, acetic acid, andphosphoric acid may be used for etching. Alternatively, molybdenum maybe deposited as the first conductive film 102, titanium, aluminum, ortungsten may be deposited as the second conductive film 110, and aliquid chemical containing hydrogen peroxide solution may be used foretching.

In the case where the second etching is performed by wet etching, it ismost preferable that a film stack in which molybdenum is deposited overaluminum to which neodymium is added be formed as the first conductivefilm 102, tungsten be deposited as the second conductive film 110. and aliquid chemical containing nitric acid at 2%, acetic acid at 10%, andphosphoric acid at 72% be used for etching. Using a liquid chemicalhaving such a composition ratio, the first conductive film 102 can beetched without the second conductive film 110 being etched. Note thatneodymium is added to the first conductive film 102 for the purpose ofreducing resistance of aluminum and preventing hillocks.

As illustrated in FIG. 17, the gate electrode layer 116 has a hornyportion (for example, a horny portion 151) in a plan view. This isbecause since the second etching for forming the gate electrode layer116 is almost isotropic, etching is performed in such a manner that thedistance d₁ between the side surface of the gate electrode layer 116 andthe side surface of the thin film stack 114 is almost uniform.

Next, the first resist mask 112 is etched; accordingly, the secondconductive film 110 is exposed and a second resist mask 118 is formed.As a means for forming the second resist mask 118 by recession of edgeof the first resist mask 112, for example, ashing using oxygen plasmacan be given. However, the means for forming the second resist mask 118by recession of edge of the first resist mask 112 is not limited tothis. Note that the case where the second resist mask 118 is formedafter the second etching has been described here; however, the presentinvention is not limited to this and the second etching may be performedafter formation of the second resist mask 118.

Next, the second conductive film 110 in the thin film stack 114 isetched using the second resist mask 118, so that the source/drainelectrode layer 120 is formed (see FIG. 2A, FIG. 5A, FIG. 5A, FIG. 11A,FIG. 14A, and FIG. 18). Here, as the etching conditions, the conditionsby which films other than the second conductive film 110 are notcorroded or eaten or are not easily corroded or eaten are selected. Inparticular, it is important that etching is performed under theconditions that the gate electrode layer 116 is not easily corroded oreaten or is not easily corroded or eaten.

Note that the source/drain electrode layer 120 forms the source wiring,the electrode which connects the thin film transistor and the pixelelectrode to each other, and one electrode of a capacitor functioning asa storage capacitor. When a source/drain electrode layer is referred toas the source/drain electrode layer 120A or a source/drain electrodelayer 120C, the source/drain electrode layer forms an electrode layerforming a source wiring; when a source/drain electrode layer is referredto as a source/drain electrode layer 120B, the source/drain electrodelayer forms an electrode layer which connects a drain electrode of thethin film transistor and the pixel electrode to each other; and when asource/drain electrode layer is referred to as a source/drain electrodelayer 120D, the source/drain electrode layer forms one electrode layerwhich forms the capacitor with the capacitor wiring. Then, thesesource/drain electrode layers are collectively referred to as thesource/drain electrode layer 120.

Note that for etching the second conductive film 110 in the thin filmstack 114, either wet etching or dry etching may be used.

Then, the impurity semiconductor film 108 and an upper portion of thesemiconductor film 106 (back channel portion) in the thin film stack 114are etched to form a source/drain region 122 (see FIG. 2B, FIG. 5B, FIG.3B, FIG. 11B, FIG. 14B, and FIG. 19). Here, as the etching conditions,the conditions by which films other than the impurity semiconductor film108 and the semiconductor film 106 are not corroded or eaten or are noteasily corroded or eaten are selected. In particular, it is importantthat etching is performed under the conditions that the gate electrodelayer 116 is not easily corroded or eaten or is not easily corroded oreaten.

Note that the etching of the impurity semiconductor film 108 and theupper portion of the semiconductor film 106 (back channel portion) inthe thin film stack 114 can be performed by dry etching or wet etching.

Then, the second resist mask 118 is removed (see FIG. 2C, FIG. 5C, FIG.8C, FIG. 11C, and FIG. 14C); accordingly, a thin film transistor iscompleted (see FIG. 2C). As described above, the thin film transistorcan be formed using one photomask.

In this specification, the steps described with reference to FIG. 2A andFIG. 2B are collectively referred to as “third etching” The thirdetching may be performed in a plurality of separate steps as describedabove or may be performed in a single step.

A second insulating film is formed to cover the thin film transistorwhich is formed in the above-described manner. Here, an example of usingthe protective film 126 as the second insulating film is described;however, a layered structure having two or more layers may be employedwithout limitation to a single layer structure. The first protectivefilm 126 can be formed in a similar manner to the first insulating film104. After that, color filter layers 128 is formed over the secondinsulating film (see FIG. 3A, FIG. 6A, FIG. 9A, FIG. 12A, and FIG. 15A).

The color filter layers 128 are formed so that surface unevenness causedby the thin film stack 114 is reduced. More specifically, the colorfilter layers are formed so that planarity of the surface over which thepixel electrode layer is later formed is improved. In this embodimentmode, the color filter layers 128 are formed so as to be embedded inregions where the thin film stack 114 and the like is not formed;however, the present invention should not construed as being limitedthereto as long as unevenness caused by the thin film stack 114 or thelike can be reduced.

As described above, unevenness of the surface over which the pixelelectrode is formed is reduced using the color filter layers;accordingly, the color filter layers are formed and planarity can beimproved by one step. Thus, planarity of the pixel electrode isimproved, which prevents orientation disorder of liquid crystal andimproves display image quality. Further, since formation of a layer forimproving planarity separately from the color filter layer is renderedunnecessary, which leads to more simplified process steps.

Note that the color filter layers 128 may be formed as appropriate by,for example, a printing method, an ink-jet method, photolithography, orthe like. For example, after resins each having a pigment correspondingto R (red), G (green), or B (blue), respectively are formed by spincoating or the like, patterning is performed by photolithography; thus,the color filter layers 128 can be formed. The stripe pattern, the deltapattern, the square pattern, or the like can be used as the pattern ofthe color filter.

Note that in the case of forming the color filter by photolithography,one photomask is used. Naturally, the color filter may be formed using amethod in which a photomask is not used.

Next, a first opening portion 130 and a second opening portion 131 areformed in the second insulating film (see FIG. 3B, FIG. 6B, FIG. 9B,FIG. 12B, and FIG. 15B). The first opening portion 130 and the secondopening portion 131 are formed so as to reach at least the surface of asource/drain electrode layer. The method for forming the first openingportion 130 and the second opening portion 131 is not limited to aparticular method and may be determined as appropriate by a practitionerin accordance with the diameter of the first opening portion 130 or thelike. For example, the first opening portion 130 and the second openingportion 131 can be formed by dry etching using a photolithographymethod.

Note that in the ease of forming the opening portions byphotolithography, one photomask is used.

Next, the pixel electrode layer 132 is formed over the second insulatingfilm (see FIG. 3C, FIG. 6C, FIG. 9C, FIG. 12C, FIG. 15C, and FIG. 20).The pixel electrode layer 132 is formed so as to be connected to thesource/drain electrode layer 120 through the opening portions.Specifically, the pixel electrode layer 132 is formed so as to beconnected to the source/drain electrode layer 120B through the firstopening portion 130 and connected to the source/drain electrode layer120D through the second opening portion 131. The pixel electrode layer132 is preferably formed using a light-transmitting conductive material.Here, as the light-transmitting conductive material, indium tin oxide(hereinafter referred to as ITO), indium oxide containing tungstenoxide, indium zinc oxide containing tungsten oxide. indium oxidecontaining titanium oxide, indium tin oxide containing titanium oxide,indium zinc oxide, indium tin oxide to which silicon oxide is added, andthe like can be given. The film of the light-transmitting conductivematerial may be formed by sputtering, CVD, or the like; however, themethod for forming the film of the light-transmitting conductivematerial is not limited to a particular method. In addition, the pixelelectrode layer 132 may have a single-layer structure or a layeredstructure in which a plurality of films are stacked.

Note that in this embodiment mode, the light-transmitting conductivematerial is used for only the pixel electrode layer 132; however, thepresent invention is not limited to this. As materials of the firstconductive film 102 and the second conductive film 110,light-transmitting conductive materials may be used.

Note that in the case of forming the pixel electrode layer 132 byphotolithography, one photomask is used.

Through the above steps, an active matrix substrate used for a liquidcrystal display device is completed. As described in this embodimentmode, the thin film transistor can be manufactured using one photomaskin such a manner that the gate electrode layer is formed utilizing sideetching, and further, the source/drain electrode layer is formed using amulti-tone mask. Further, unevenness of the surface over which the pixelelectrode is formed is reduced using color filter layers; accordingly,the color filter layers are formed and planarity can be improved by onestep. Accordingly, more simplified process steps are realized.

Note that although not shown in this embodiment mode, after formation ofthe color filter layers and before formation of the pixel electrodelayer, an overcoat layer may be formed. The formation of the overcoatlayer can further improve planarity of a surface over which the pixelelectrode is formed. In addition, part of a material included in thecolor filter layers can be prevented from entering a liquid crystalmaterial. For the overcoat layer, a thermosetting material which mainlycontains acrylic resin or epoxy resin is used.

The thin film transistor manufactured using the manufacturing method ofthe present invention has a structure including a gate insulating filmover a gate electrode layer, a semiconductor layer over the gateinsulating film, a source region and a drain region over thesemiconductor layer, a source electrode and a drain electrode over thesource region and the drain region, and a cavity adjacent to a sidesurface of the gate electrode layer (see FIG. 3C). With the cavityformed adjacent to the side surface of the gate electrode layer, a thinfilm transistor with low leakage current at an end portion of the gateelectrode layer can be manufactured.

Here, a terminal connection portion of the active matrix substratemanufactured in the above-described steps will be described withreference to FIG. 22, FIG. 23, and FIGS. 24A to 24C.

FIG. 22 is a plan view and FIG. 23 and FIGS. 24A to 24C arecross-sectional views of a terminal connection portion on the gatewiring side and a terminal connection portion on the source wiring sideof the active matrix substrate manufactured in the above-describedsteps.

FIG. 22 is a plan view of the gate wiring and the source wiring whichare extended from the pixel portion, in the terminal connection portionon the gate wiring side and the terminal connection portion on thesource wiring side.

FIG. 23 is a cross-sectional view taken along line X-X′ in FIG. 22. Thatis, FIG. 23 is a cross-sectional view of the terminal connection portionon the gate wiring side. In FIG. 23, only the gate electrode layer 116is exposed. A terminal portion is connected to the region in which thegate electrode layer 116 is exposed.

FIGS. 24A to 24C are cross-sectional views taken along line Y-Y′ in FIG.22. That is, FIGS. 24A to 24C are cross-sectional views of the terminalconnection portion on the source wiring side. In the cross section alongline Y-Y′ illustrated in FIGS. 24A to 24C, the gate electrode layer 116and the source/drain electrode layer 120 are connected to each otherthrough the pixel electrode layer 132. FIGS. 24A to 24C illustratevarious modes of connection between the gate electrode layer 116 and thesource/drain electrode layer 120. Any of these modes or modes other thanthose illustrated in FIGS. 24A to 24C may be used for the terminalconnection portion in a display device according to the presentinvention. With the structure in which the source/drain electrode layer120 is connected to the gate electrode layer 116, the height of theterminal connection portion can be made almost uniform.

Note that the number of opening portions is not limited to that ofopening portions in FIGS. 24A to 24C. Not only one opening portion butalso a plurality of opening portions may be provided for one terminal.In the case where a plurality of opening portions are provided for oneterminal, even when any of the opening portions is not formed favorablydue to insufficient etching for forming the opening portion, electricalconnection can be realized at the other opening portion. Further, evenin the case where all the opening portions are formed without anyproblems, the contact area can be made larger and contact resistance canbe reduced, which is preferable.

In FIG. 24A, electrical connection is realized in such a manner that anend portion of the protective film 126 is removed by etching or the liketo expose the gate electrode layer 116 and the source/drain electrodelayer 120, and the pixel electrode layer 132 is formed over the exposedregion. The plan view illustrated in FIG. 22 corresponds to the planview of FIG. 24A.

Note that the formation of the region in which the gate electrode layer116 and the source/drain electrode layer 120 are exposed can beperformed at the same time as the formation of the first opening portion130 and the second opening portion 131.

In FIG. 24B, electrical connection is realized in such a manner that athird opening portion 160A is provided in the protective film 126, endportions of the first protective film 126 and the color filter layers128 are removed by etching or the like to expose the gate electrodelayer 116 and the source/drain electrode layer 120, and the pixelelectrode layer 132 is formed over the exposed region.

Note that the formation of the third opening portion 160A and theformation of the region in which the gate electrode layer 116 is exposedcan be performed at the same time as the formation of the first openingportion 130 and the second opening portion 131.

In FIG. 24C, electrical connection is realized in such a manner that athird opening portion 160B and a fourth opening portion 161 are providedin the protective film 126 and the color filter layers 128 to expose thegate electrode layer 116 and the source/drain electrode layer 120, andthe pixel electrode layer 132 is formed over the exposed region. Here,end portions of the protective film 126 and the color filter layers 128are removed by etching or the like similarly to FIGS. 24A and 24B, andthis etched region is used as a terminal connection portion.

Note that the formation of the third opening portion 160B and the fourthopening portion 161 and the formation of the region in which the gateelectrode layer 116 is exposed can be performed at the same time as theformation of the first opening portion 130 and the second openingportion 131.

Next, a method of manufacturing a liquid crystal display device usingthe above active matrix substrate will be described. That is, a cellprocess and a module process will be described. Note that the cellprocess and the module process are not particularly limited in themethod of manufacturing a liquid crystal display device of the presentinvention.

In the cell process, the active matrix substrate manufactured in theabove-described steps and a substrate opposite to the active matrixsubstrate (hereinafter referred to as a counter substrate) are attachedto each other and liquid crystal is injected. First, a manufacturingmethod of the counter substrate will be briefly described below. Notethat, although not mentioned, a film formed on the counter substrate maybe in a single layer structure or a layered structure.

First, a light-blocking layer is formed over a substrate, and then, arib is formed over the pixel electrode layer. Note that after thelight-blocking layer is formed, an insulating film for improvingplanarity is formed before the electrode layer is formed. The formationof an insulating film for improving planarity improves planarity of asurface on which the electrode layer is formed; thus, orientationdisorder of liquid crystal can be suppressed.

As the light-blocking layer, a film of a material having alight-blocking property is selectively formed. As the material having alight-blocking property, for example, an organic resin containing ablack resin (carbon black) can be used. Alternatively, a film stackwhich includes a film of a material containing chromium as its maincomponent may be used. The film of a material containing chromium as itsmain component means a film containing chromium, chromium oxide, orchromium nitride. The material used for the light-blocking layer is notparticularly limited as long as it has a light-blocking property. Inorder to selectively form the film of a material having a light-blockingproperty, photolithography or the like is employed.

In the case where an insulating film for improving planarity is formed,it may be formed, for example, by spin coating or the like using amaterial of photosensitive polyimide, photosensitive acrylic, aphotosensitive epoxy resin, or the like. Note that the present inventionis not limited to these materials and the formation method.

The electrode layer can be formed in a similar manner to the pixelelectrode layer 132 included in the active matrix substrate. Note thatsince selective formation is not necessary, the pixel electrode layermay be formed over the entire surface.

The rib formed over the electrode is an organic resin film formed with apattern for the purpose of widening the viewing angle. Note that the ribdoes not need to be formed if not particularly necessary.

Further, before or after formation of the rib, a post spacer (columnarspacer) may be formed as a spacer. The post spacer means a structuralobject formed at a constant interval on the counter substrate in orderto keep the gap between the active matrix substrate and the countersubstrate uniform. In the case of using a bead spacer (sphericalspacer), the post spacer need not be formed.

Next, an alignment film is formed on the active matrix substrate and thecounter substrate. Formation of the alignment film is performed, forexample, in such a manner that polyimide resin or the like is melted inan organic solvent; this solution is applied by a coating method, a spincoating method, or the like; and then the solution is dried and baked.The thickness of the formed alignment film is generally approximatelyequal to or greater than about 50 nm and equal to or less than about 100μm. Rubbing treatment is performed on the alignment film to align liquidcrystal molecules with a certain pretilt angle. The rubbing treatment isperformed, for example, by rubbing an alignment film with a shaggy clothsuch as a velvet.

Then, the active matrix substrate and the counter substrate are attachedwith a sealant. In the case where a post spacer is not provided on thecounter substrate, a bead spacer may be dispersed in a desired regionand attachment may be performed.

Next, a liquid crystal material is injected in a space between theactive matrix substrate and the counter substrate, which are attached toeach other. After injection of the liquid crystal material, an inlet forinjection is sealed with an ultraviolet curing resin or the like.Alternatively, after dropping a liquid crystal material, the activematrix substrate and the counter substrate may be attached to eachother.

Next, a polarizing plate is attached to both surfaces of a liquidcrystal cell, which is formed by attachment of the active matrixsubstrate and the counter substrate. Thus, the cell process is finished.

Next, as the module process, a flexible printed circuit (FPC) isconnected to an input terminal (in FIGS. 24A to 24C, the exposed regionof the gate electrode layer 116) of the terminal portion. The FPC has awiring formed of a conductive film over an organic resin film ofpolyimide or the like, and is connected to the input terminal through ananisotropic conductive paste (hereinafter referred to as an ACP). TheACP includes a paste functioning as an adhesive and particles platedwith gold or the like to have a conductive surface, which have adiameter of several tens of micrometers to several hundreds ofmicrometers. When the particles mixed in the paste are in contact withthe conductive layer over the input terminal and the conductive layerover the terminal connected to the wiring formed in the FPC, electricalconnection therebetween is realized. Alternatively, after connection ofthe FPC, a polarizing plate may be attached to the active matrixsubstrate and the counter substrate. Through the above steps, a liquidcrystal display device can be manufactured.

In accordance with the present invention, the number of steps formanufacturing a liquid crystal display device can be significantlyreduced. This is because thin film transistors can be manufactured usingone photomask (multi-tone mask). Further, a color filter is used toimprove planarity; thus, an insulating film or the like is notnecessarily formed separately, which leads to reduction in the number ofsteps. Still further, unevenness caused by thin film transistors isreduced, so that planarity of the pixel electrode is improved andorientation disorder of liquid crystal can be suppressed.

In the present invention, the number of steps for manufacturing a thinfilm transistor can be significantly reduced without using a complicatedmethod such as backside exposure, resist reflow, a lift-off method, orthe like. Therefore, the number of steps for manufacturing a liquidcrystal display device can be significantly reduced without using acomplicated process.

Moreover, the number of steps for manufacturing a liquid crystal displaydevice can be significantly reduced while electrical characteristics ofthe thin film transistor are maintained. Furthermore, manufacturing costcan be significantly reduced.

Embodiment Mode 2

In this embodiment mode, a manufacturing method of a thin filmtransistor and a manufacturing method of a display device according tothe present invention, which are different from those of Embodiment Mode1, will be described. Specifically, a manufacturing method of a thinfilm transistor which is similar to that in Embodiment Mode 1, withoutusing a multi-tone mask will be described with reference to FIGS. 26A,26B, and 26C, FIGS. 27A, 27B, and 27C, FIG. 28, FIG. 29, and FIG. 30.

FIGS. 26A, 26B, and 26C correspond to FIG. 1A, FIG. 1C, and FIG. 2A ofEmbodiment Mode 1. FIGS. 27A, 27B, and 27C correspond to FIG. 10A, FIG.10C, and FIG. 11A of Embodiment Mode 1. FIG. 28, FIG. 29, and FIG. 30correspond to FIG. 16, FIG. 17, and FIG. 18 of Embodiment Mode 1. Thecross-sectional views taken along line A-A′ illustrated in FIG. 28, FIG.29, and FIG. 30 correspond to FIGS. 26A, 26B, and 26C, and thecross-sectional views taken along line D-D′ illustrated in FIG. 28, FIG.29, and FIG. 30 correspond to FIGS. 27A, 27B, and 27C.

First, similar to Embodiment Mode 1, a first conductive film 102, afirst insulating film 104, a semiconductor film 106, an impuritysemiconductor film 108, and a second conductive film 110 are formed overa substrate 100. Materials thereof and formation methods thereof aresimilar to those in Embodiment Mode 1.

Then, a first resist mask 170 is formed over the second conductive film110 (see FIG. 26A and FIG. 27A). The first resist mask 170 is differentfrom the first resist mask 112 of Embodiment Mode 1 and is formed so asto have an almost uniform thickness without a recessed portion beingprovided. That is, the first resist mask 170 is formed without using amulti-tone mask.

Next, first etching is performed using the first resist mask 170. Thatis, the first conductive film 102, the first insulating film 104, thesemiconductor film 106, the impurity semiconductor film 108, and thesecond conductive film 110 are patterned by etching to form a thin filmstack 114 over the first conductive film 102 (see FIG. 28).

Next, second etching is performed in a similar manner to Embodiment Mode1 to form a gate electrode layer 116 (see FIG. 26C, FIG. 27C, and FIG.29).

Here, the conditions of the second etching are similar to those of thesecond etching of Embodiment Mode 1. Then, after the second etching, thefirst resist mask 170 is removed.

Next, a second resist mask 171 is formed over the thin film stack 114,and a source/drain electrode layer 120 is formed using the second resistmask 171. The etching conditions or the like are similar to those ofEmbodiment Mode 1. Further, steps following this are similar to those ofEmbodiment Mode 1.

As described in this embodiment mode above, a thin film transistor canbe manufactured without using a multi-tone mask. Accordingly, a liquidcrystal display device can be manufactured. Note that the number ofmasks to be used is increased by one, as compared to that of EmbodimentMode 1.

Note that the manufacturing method of a thin film transistor and amanufacturing method of a display device according to this embodimentmode are similar to those of Embodiment Mode 1 except for the pointdescribed above. Therefore, effects similar to those offered by themanufacturing method of a thin film transistor and the manufacturingmethod of a display device of Embodiment Mode 1 can be naturallyobtained; however, the number of masks used is increased by one. Inother words, according to this embodiment mode, a thin film transistorcan be manufactured using two photomasks. Accordingly, the number ofphotomasks to be used is reduced as compared to conventional methods,and the number of steps for manufacturing thin film transistors can bereduced. Further, the number of steps for manufacturing a liquid crystaldisplay device can be reduced. Furthermore, thin film transistors and aliquid crystal display device can be manufactured with high yield at lowcost.

Note that the thin film transistor manufactured using the manufacturingmethod of this embodiment mode has a structure including a gateinsulating film over a gate electrode layer, a semiconductor layer overthe gate insulating film, a source region and a drain region over thesemiconductor layer, a source electrode and a drain electrode over thesource region and the drain region, and a cavity adjacent to a sidesurface of the gate electrode layer. With the cavity formed adjacent tothe side surface of the gate electrode layer, a thin film transistorwith low leakage current at an end portion of the gate electrode layercan be manufactured.

Embodiment Mode 3

In this embodiment mode, a manufacturing method of a thin filmtransistor and a manufacturing method of a liquid crystal display deviceaccording to the present invention, which are different from those ofEmbodiment Modes 1 and 2, will be described. Specifically, a mode inwhich a first conductive film 102 is etched by the first etching whichis described in Embodiment Modes 1 and 2 will be described withreference to FIGS. 31A to 31C, FIGS. 32A to 32C, FIGS. 33A to 33C, FIGS.34A to 34C, FIGS. 35A to 35C, and FIG. 36.

FIGS. 31A to 31C correspond to FIGS. 1A to 1C of Embodiment Mode 1.FIGS. 32A to 32C correspond to FIGS. 4A to 4C of Embodiment Mode 1.FIGS. 33A to 33C correspond to FIGS. 7A to 7C of Embodiment Mode 1.FIGS. 34A to 34C correspond to FIGS. 10A to 10C of Embodiment Mode 1.FIGS. 35A to 35C correspond to FIGS. 13A to 13C of Embodiment Mode 1.FIG. 36 corresponds to FIG. 16 of Embodiment Mode 1.

First, similar to Embodiment Mode 1, a first conductive film 102, afirst insulating film 104, a semiconductor film 106, an impuritysemiconductor film 108, and a second conductive film 110 are formed overa substrate 100. Materials thereof and formation methods thereof aresimilar to those in Embodiment Mode 1.

Then, a first resist mask 112 is formed over the second conductive film110 (see FIG. 31A, FIG. 32A, FIG. 33A, FIG. 34A, and FIG. 35A). Thefeatures of the first resist mask 112 are similar to those of EmbodimentMode 1.

Next, first etching is performed using the first resist mask 112. Thatis, the first conductive film 102, the first insulating film 104, thesemiconductor film 106, the impurity semiconductor film 108, and thesecond conductive film 110 are patterned by etching to form a thin filmstack 114 and an etched first conductive film 115 (see FIG. 31B, FIG.32B, FIG. 33B, FIG. 34B, FIG. 35B, and FIG. 36).

As described above, this embodiment mode is different from EmbodimentMode 1 in that the first conductive film 102 is processed by the firstetching so that the etched first conductive film 115 is formed.

Next, by second etching, the etched first conductive film 115 isprocessed into a gate electrode layer 116 (see FIG. 31C, FIG. 32C, FIG.33C, FIG. 34C, and FIG. 35C).

Here, the conditions and the like of the second etching are similar tothose of the second etching of Embodiment Mode 1, except for thefollowing point.

In Embodiment Mode 1, the region that should be removed of the firstconductive film 102 needs to be completely removed only by the secondetching. Note that the region that should be removed of the firstconductive film 102 means a region other than the region where the gateelectrode layer 116 is formed.

Here, the distance d₁ between the side surface of the thin film stack114 and the side surface of the gate electrode layer 116 depends on thethickness of the first conductive film 102. The second etching isetching in which side etching is performed and is almost isotropicetching (so-called chemical etching). Therefore, in the method describedin Embodiment Mode 1, in the case where the distance d₁ is made smallerthan the thickness of the first conductive film 102, it is difficult tocompletely remove the region of the first conductive film 102, whichshould be removed.

On the other hand, as described above, the first conductive film 115 isformed by processing the first conductive film 102 by the first etchingand the gate electrode layer 116 is formed by the second etching; thus,the distance d₁ can be made smaller than the thickness of the firstconductive film 102. That is, the distance d₁ can be controlledindependently of the thickness of the first conductive film 102, therebyincreasing layout design flexibility.

Note that steps following the second etching are similar to those ofEmbodiment Mode 1. That is, by combining the method described inEmbodiment Mode 1 with the method described in this embodiment mode, athin film transistor can be manufactured. Specifically, thin filmtransistors are manufactured using one photomask by forming a gateelectrode layer by side etching, and further, forming a source/drainelectrode layer using a multi-tone mask.

As described above in this embodiment mode, the first conductive film102 is processed by the first etching; thus, the distance d₁ between theside surface of the thin film stack 114 and the side surface of the gateelectrode layer 116 can be designed independently of the thickness ofthe first conductive film 102, thereby increasing the freedom of layoutdesign.

Note that the manufacturing method of a thin film transistor and amanufacturing method of a liquid crystal display device according tothis embodiment mode are similar to those of Embodiment Mode 1 exceptfor the point described above. Therefore, effects similar to themanufacturing method of a thin film transistor and a manufacturingmethod of a display device of Embodiment Mode 1 can be obtainednaturally.

Note that this embodiment mode may be implemented in combination withEmbodiment Mode 2.

Embodiment Mode 4

In this embodiment mode, a manufacturing method of thin film transistorand a manufacturing method of a liquid crystal display device accordingto the present invention, which have a feature in a method formanufacturing color filter layers will be described. Specifically, anembodiment of selectively forming color filters in a manufacturingprocess of color filter layers, which has been described in EmbodimentMode 1 to Embodiment Mode 3, or the like, by a printing method or anink-jet method will be described with reference to FIGS. 37A, 37B, and37C, and FIGS. 38A and 38B.

Note that FIG. 37A corresponds to FIG. 3A, FIG. 37B corresponds to FIG.6A, and FIG. 37C corresponds to FIG. 9A. Further, FIG. 38A correspondsto FIG. 12A and FIG. 38B corresponds to FIG. 15A.

First, as in Embodiment Mode 1, a thin film stack 114 and a gateelectrode layer 116 are formed to the desired shape, and the secondresist mask 118 is removed (see FIG. 2C, FIG. 5C, FIG. 8C, FIG. 11C, andFIG. 14C).

Then, a second insulating film is formed to cover the thin filmtransistor which is formed through the above-described steps. Here, theprotective film 126 is used as the second insulating film; however, theprotective film 126 may have a layered structure having two or morelayers without limitation to such a single-layer structure. After that,the color filter layers 128 are formed over the second insulating film(see FIG. 37A, FIG. 37B, FIG. 37C, FIG. 38A, and FIG. 38B).

As already described, in this embodiment mode, the color filter layers128 are formed using a printing method or an ink-jet method. Here, thethin film stack 114 of the present invention has a layered structureincluding the first conductive film 102, the first insulating film 104,the semiconductor film 106, the impurity semiconductor film 108, and thesecond conductive film 110. Accordingly, the thickness of the thin filmstack 114 to be a source wiring or a gate wiring is larger as comparedwith the case of using a conventional manufacturing method. By utilizingthis, the color filter layers 128 can be easily formed separately.

For example, in the case where the color filter layers 128 of respectivecolors of R (red), G (green), and B (blue) are formed to extend in thedirection parallel to source wirings, a color filter layer 128 of acolor is formed in a region sandwiched between the source wirings(hereinafter, referred to as a region between source wirings), and acolor filter layer 128 of another color is formed between an adjacentregion between source wirings. A printing method or an ink-jet methodare methods in which formation is performed by dropping droplets;however, with the source wirings formed from the thin film stack 114,unnecessary expansion of droplets can be prevented, so that fabricationaccuracy of the color filter layers 128 can be improved.

Note that the color filter layers 128 have an effect of reducing surfaceunevenness caused by the thin film stack 114 or the like. In order toeffectively utilize this effect, in this embodiment mode, a structure isemployed in which color filter layers 128 are also formed in a regionother than a region where the pixel electrode layer 132 is to be laterformed. However, if the effect of reducing surface unevenness is notconsidered important, a structure in which the color filter layer 128 isformed in a region exactly below the region where the pixel electrodelayer 132 is formed may be employed.

Further, after formation of the color filter layers and before formationof the pixel electrode layer, an overcoat layer may be formed. Theformation of the overcoat layer can further improve planarity of asurface over which the pixel electrode is formed. In addition, part of amaterial included in the color filter layers can be prevented fromentering a liquid crystal material. For the overcoat layer, athermosetting material which mainly contains acrylic resin or epoxyresin is used.

As described above, the color filter layers 128 are formed separately byutilizing unevenness caused by the thin film stack 114; thus, colorseparation accuracy of the color filter layers 128 is improved. Further,since unevenness of the surface over which the pixel electrode is formedcan be reduced, the color filter layers are formed and planarity can beimproved by one step. By improving planarity of the pixel electrode,orientation disorder of liquid crystal is improved, and image displayquality is improved. Further, since steps of patterning for forming thecolor filter layers 128 or the like are not necessary, the number ofsteps can be further reduced.

Since subsequent steps are similarly performed by the methods describedin Embodiment Mode 1 to Embodiment Mode 3, the description is omittedhere. This embodiment mode can be combined with Embodiment Mode 1 toEmbodiment Mode 3 as appropriate.

Embodiment Mode 5

In this embodiment mode, electronic appliances in each of which a liquidcrystal display device manufactured using any of the methods describedin Embodiment Modes 1 to 4 is incorporated as a display portion will bedescribed with reference to FIGS. 39A and 39B, FIG. 40, and FIGS. 41A to41C. As such electronic appliances, for example, cameras such as videocameras or digital cameras; head mounted displays (goggle typedisplays); projectors; car navigation systems; car stereos; personalcomputers; and portable information terminals (such as mobile computers,mobile phones, and e-book readers) can be given.

FIG. 39A illustrates a television unit. A television unit illustrated inFIG. 39A can be completed by incorporating a liquid crystal displaydevice manufactured using the present invention into a housing. A mainscreen 223 is formed using the liquid crystal display devicemanufactured by any of the manufacturing methods described in EmbodimentModes 1 to 3, and a speaker portion 229, operation switches, and thelike are provided as its accessory equipment.

As illustrated in FIG. 39A, a liquid crystal display device 222manufactured by any of the manufacturing methods described in EmbodimentModes 1 to 3 is incorporated into a housing 221, and general TVbroadcast can be received by a receiver 225. When the television unit isconnected to a communication network by wired or wireless connectionsvia a modem 224, one-way (from a sender to a receiver) or two-way(between a sender and a receiver or between receivers) datacommunication can be performed.

The television unit can be operated using switches incorporated into thehousing or by a remote controller 226 which is separate from thehousing. A display portion 227 which displays output data may also beprovided for the remote controller 226.

Further, the television unit may include a subscreen 228 provided fordisplaying channels, volume, and the like, in addition to the mainscreen 223.

FIG. 40 is a block diagram of a main structure of a television unit. Apixel portion 251 is formed in a display region. A signal line drivercircuit 252 and a scan line driver circuit 253 may be implemented by aCOG method.

As structures of external circuits, a video signal amplifier circuit 255for amplifying a video signal among signals received by a tuner 254, avideo signal processing circuit 256 for converting signals output fromthe video signal amplifier circuit 255 into chrominance signalscorresponding to colors of red, green, and blue, a control circuit 257for converting the video signal into a signal which meets inputspecifications of a driver circuit, and the like are provided on theinput side of the video signal. The control circuit 257 outputs signalsto each of the scan line side and the signal line side. In the case ofdigital drive, a signal dividing circuit 258 may be provided on thesignal line side to supply an input digital signal divided into m (m isan integer) pieces.

Among the signals received by the tuner 254, audio signals aretransmitted to an audio signal amplifier circuit 259, and an outputthereof is supplied to a speaker 263 through an audio signal processingcircuit 260. A control circuit 261 receives control data on receivingstation (receiving frequency) and volume from an input unit 262 andtransmits signals to the tuner 254 and the audio signal processingcircuit 260.

When a liquid crystal display device or display device manufactured byany of the manufacturing methods which are described in Embodiment Modes1 to 3, is applied to the main screen 223 and the subscreen 228,productivity of television units can be increased.

Note that the above structure is not limited to the television unit andcan also be applied to a large-size display medium such as aninformation display board at a station, an airport, and the like, or anadvertisement display board on the street, as well as a monitor of apersonal computer. In accordance with the present invention,productivity for these display mediums can be improved.

A mobile computer illustrated in FIG. 39B includes a main body 231, adisplay portion 232, and the like. When the liquid crystal displaydevice manufactured by any of the methods which are described inEmbodiment Modes 1 to 3, is applied to the display portion 232,productivity for computers can be increased.

FIGS. 41A to 41C illustrate a structural example of a portableelectronic device 300 having functions as a telephone and an informationterminal. Here, FIG. 41A is a front view, FIG. 41B is a back view, andFIG. 41C is a developed view. The portable electronic device 300 hasfunctions as both a telephone and an information terminal and is anelectronic device so-called a smartphone which is capable of variousdata processing besides voice call.

The portable electronic device 300 includes housings 301 and 302. Thehousing 301 is provided with a display portion 311, a speaker 312, amicrophone 313, operation keys 314, a pointing device 315, a lens 316for camera, an external connection terminal 317, and the like. Thehousing 302 is provided with a keyboard 321, an external memory slot322, a lens 323 for camera, a light 324, an earphone port 325, and thelike. In addition, an antenna is incorporated in the housing 301. Inaddition to the above-described structure, a wireless IC chip, a smallsize memory device, or the like can be built therein.

The display portion 311 includes a semiconductor device according to thepresent invention. An image displayed (and direction in which the imageis displayed) in the display portion 311 variously changes depending onthe usage mode of the portable electronic device 300. Moreover, sincethe display portion 311 and the lens 316 for camera are provided on thesame plane, voice call with images (so-called videophone) is possible.Note that the speaker 312 and the microphone 313 can be used not onlyfor voice call but also for recording, reproducing, or the like. In thecase where a still image and a moving image are shot by using the lens323 for camera (and the light 324), the display portion 311 is used as afinder. The operation keys 314 are used for operation of incoming andoutgoing calls, information input for electronic mail or the like,scrolling of a screen, cursor motion, and the like.

The housings 301 and 302 superimposed on each other (FIG. 41A) slide andcan be developed as illustrated in FIG. 41C, so that the portableelectronic device 300 can be used as an information terminal. In thatcase, smooth operation with the keyboard 321 and the pointing device 315can be performed. The external connection terminal 317 can be connectedto various cables such as an AC adopter or a USB cable, so that theportable electronic device 300 can be charged or can perform datacommunication with a computer or the like. Moreover, by inserting arecording medium into the external memory slot 322, the portableelectronic device 300 can deal with storing and moving a large capacityof data. In addition to the above-described functions, a function ofwireless communication by using electromagnetic waves such as infraredrays, a function of receiving television, and the like may be included.By using the invention disclosed in this specification, a portableelectronic device having high reliability and high performance can beprovided at low cost.

Since various electronic devices described in this embodiment mode canbe manufactured by any of the manufacturing methods of a liquid crystaldisplay device and a display device described in Embodiment Modes 1 to3, productivity of these electronic devices can be increased.

Accordingly, using the present invention, manufacturing cost of theseelectronic devices can be significantly reduced.

This application is based on Japanese Patent Application serial no.2008-046601 filed with Japan Patent Office on Feb. 27, 2008, the entirecontents of which are hereby incorporated by reference.

EXPLANATION OF REFERENCE

-   100: substrate, 102: conductive film, 104: insulating film, 106:    semiconductor film, 108: impurity semiconductor film, 110:    conductive film, 112: resist mask, 114: thin film laminate, 115:    conductive film, 116: gate electrode layer, 116A: gate electrode    layer, 116B: gate electrode layer, 116C: gate electrode layer, 116D:    gate electrode layer, 118: resist mask, 120: source/drain electrode    layer, 120A: source/drain electrode layer, 120B: source/drain    electrode layer, 120C: source/drain electrode layer, 120D:    source/drain electrode layer, 122: source/drain region, 126:    protective film, 128: color filter layers, 130: opening portion,    131: opening portion, 132: pixel electrode layer, 140: gray-tone    mask, 141: substrate, 142: light-blocking portion, 143: slit    portion, 145: half-tone mask, 146: substrate, 147:    semi-light-transmitting portion, 148: light-blocking portion, 151:    horny portion, 160A: opening portion, 160B: opening portion, 161:    opening portion, 170: resist mask, 171: resist mask, 221: housing,    222: liquid crystal display device, 223: main screen, 224: modem,    225: receiver, 226: remote controller, 227: display portion, 228:    subscreen, 229: speaker portion, 231: main body, 232: display    portion, 251: pixel portion, 252: signal line driver circuit, 253:    scan line driver circuit, 254: tuner, 255: video signal amplifier    circuit, 256: video signal processing circuit, 257: control circuit,    258: signal dividing circuit, 259: audio signal amplifier circuit    260: audio signal processing circuit, 261: control circuit, 262:    input unit, 263: speaker, 300: portable electronic device, 301:    housing, 302: housing, 311: display portion, 312: speaker, 313:    microphone, 314: operation keys, 315: pointing device, 316: lens for    camera, 317: external connection terminal, 321: keyboard, 322:    external memory slot, 323: lens for camera, 324: light, and 325:    earphone port.

1. A manufacturing method of a liquid crystal display device, comprisingthe steps of: forming a first conductive film; forming an insulatingfilm over the first conductive film; forming a semiconductor film overthe insulating film; forming an impurity semiconductor film over thesemiconductor film; forming a second conductive film over the impuritysemiconductor film; forming a first resist mask over the secondconductive film; first etching the insulating film, the semiconductorfilm, the impurity semiconductor film, and the second conductive filmusing the first resist mask to expose at least a surface of the firstconductive film; second etching a portion of the first conductive filmto form a gate electrode layer in such manner that a width of the gateelectrode is narrower than a width of the insulating film; forming asecond resist mask over the second conductive film; third etching thesecond conductive film, the impurity semiconductor film, and a part ofthe semiconductor film using the second resist mask to form source anddrain electrode layers, source and drain region layers, and asemiconductor layer; after removing the second resist mask, forming asecond insulating film over the source electrode layer, the drainelectrode layer, the source region layer, the drain region layer, andthe semiconductor layer; forming a color filter over the secondinsulating film; and forming a pixel electrode layer over the colorfilter.
 2. A manufacturing method of a liquid crystal display device,comprising the steps of: forming a first conductive film; forming aninsulating film over the first conductive film; forming a semiconductorfilm over the insulating film; forming an impurity semiconductor filmover the insulating film; forming a second conductive film over theimpurity semiconductor film; forming a first resist mask including arecessed portion, over the second conductive film; first etching theinsulating film, the semiconductor film, the impurity semiconductorfilm, and the second conductive film using the first resist mask toexpose at least a surface of the first conductive film; second etching aportion of the first conductive film to form a gate electrode layer insuch manner that a width of the gate electrode is narrower than a widthof the insulating film; forming a second resist mask by etching therecessed portion of the first resist mask to expose a part of the secondconductive film overlapping with the recessed portion of the firstresist mask; third etching the second conductive film, the impuritysemiconductor film, and a part of the semiconductor film using thesecond resist mask to form a source and drain electrode layer, sourceand drain region layers, and a semiconductor layer; after removing thesecond resist mask, forming a second insulating film over the sourceelectrode layer, the drain electrode layer, the source region layer, thedrain region layer, and the semiconductor layer; forming a color filterover the second insulating film; and forming a pixel electrode layerover the color filter.
 3. The manufacturing method of a liquid crystaldisplay device according to claim 1 or 2, wherein the second etching isperformed after forming the second resist mask.
 4. The manufacturingmethod of a liquid crystal display device according to claim 2, whereinthe first resist mask is formed using a multi-tone mask.
 5. Themanufacturing method of a liquid crystal display device according toclaim 1 or 2, wherein the first etching is dry etching, and wherein thesecond etching is wet etching.
 6. A liquid crystal display devicecomprising: a gate electrode on an insulating surface; a firstinsulating film over the gate electrode; a semiconductor layer over thefirst insulating film; an impurity semiconductor layer over thesemiconductor layer; a conductive film over the impurity semiconductorlayer; a second insulating film over the conductive film; a color filterover the second insulating film; and a pixel electrode layer over thecolor filter, wherein a cavity is formed adjacent to the gate electrodeand between the first insulating film and the insulating surface.
 7. Aliquid crystal display device according to claim 6, wherein thesemiconductor layer has a first recessed portion which is a channelregion.
 8. A liquid crystal display device according to claim 6, whereinthe semiconductor layer has a second recessed portion which overlapswith the cavity.